New Report Tracks Decades of Climate Change

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In May 2010, the temperature in Pakistan soared to more than 128 degrees – the hottest temperature ever recorded in Asia. Just a few months later, extreme monsoons left more than a fifth of the country underwater. Around the same time, Russian authorities declared the worst heat wave in 1,000 years; tens of thousands died as heat and smoke from wildfires overwhelmed Moscow.

Floods, droughts and heat records grab headlines, but it can be hard to know what they mean. We've all heard that while climate change makes extreme weather more likely, it's difficult to tie any particular weather event directly to climate change. When it comes to weather, a certain amount of out-of-the-ordinary is ordinary. So how do we know when extreme weather is the result of natural variations and when it's a sign of something more?

A new report from the World Meteorological Organization tries to contextualize the headlines of recent years by taking the long view – considering all those heat waves, droughts and storms not as single events, but across decades. "A decade is the minimum possible timeframe for meaningful assessments of climate change," said WMO Secretary-General Michel Jarraud in a statement.

2010's brutal summer, it turns out, capped what the study calls "a decade of climate extremes." With just one exception, every year between 2001 and 2010 was among the top 10 hottest on record. More than nine in 10 nations reporting data experienced their hottest decade ever; not a single nation reported decadal temperatures below the average. The decade was also the second wettest in a century –2010 was the globe's wettest year ever – but also saw severe drought in much of the world.

And Pakistan and Russia weren't alone in facing deadly weather. Remember 2003's heat wave in Europe, the continent's worst since the 1500s, which killed as many as 70,000 people? Hurricane Katrina? Cyclone Nargis?

Natural climate variability can explain some of the decade's extremes, the report cautions, but human-induced climate change also played a role. That role is even more visible when you look at extreme weather events within the context of an extreme decade.

The report also provides an even longer view: a decade-by-decade comparison of average temperatures across the globe (combined from land and sea temperatures from three different sources), with any spikes from freak weather averaged out by a more complete set of data. Instead, we see an unmistakable trend: up and up.

It's the extreme events that make headlines, but it's the long view that should make us worried.